With regards to simulating the response of the laser pulses relevant to pump-probe
spectroscopies, real-time (RT) formalism offers a straightforward
approach [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, [12]}, [13]}, [14]}, [15]}, [16]}, [17]}
over response theory based methods as the former is applicable for a large
range of field intensities, and resembles the experimental setup in a natural
way.
Addressing core level spectroscopies has added complexities, as
it requires the inclusion of scalar (SC) and spin-orbit (SO) relativistic
effects.
Therefore, the extension of the RT framework [18]} to the relativistic regime was also formulated recently
both at the four-component (4c) [19]}, [20]}, [21]} and two-component (2c) [22]}, [23]}, [24]} level.
